If it were possible to remove blood from portions of blood vessels, certain intra-arterial procedures could be performed under direct vision which would greatly enhance the procedures' effectiveness and success rate. For instance, it would make intra-arterial laser removal of obstructing plaque much easier and safer. It would also greatly improve the efficacy and safety of treating arteriosclerosis by phototheraphy.
U.S. Pat. No. 3,870,072 to Lindemann and U.S. Pat. No. 4,258,721 to Parent, et al. both disclose the concept of injecting carbon dioxide into a human body. Lindemann discusses carbon dioxide being absorbed by the blood. However, neither patent teaches the concept of injecting carbon dioxide into a blood vessel for clearing the blood to conduct a medical procedure. U.S. Pat. No. 4,648,386 teaches the use of a laser with pressurized gas but does not suggest the present invention.
Many intra-arterial procedures are now done under fluoroscopic control. Catheters impregnated with radio opaque materials are introduced into arteries and visualized as to their position by observing the radio opaque "tags". Another procedure called balloon catheter angioplasty of arteries is conducted by outlining a ballooned segment of a catheter with radio-opaque markers. The balloon is positioned in the area of a blood vessel obstruction, and the catheter balloon is inflated to stretch open the obstruction. This procedure has not been totally successful in that the obstruction sometimes immediately re-occurs due to swelling resulting from the trauma of stretching the vessel. The obstruction may also re-occur in the immediate post-operative period, requiring immediate open operative intervention, such as a bypass surgical procedure, which is one of the procedures balloon angioplasty was designed to obviate in the first place.
It has also known that lasers of various types can be used to irradiate and remove plaque, blood clots and other obstructions such as scar tissue in blood vessels. Lasers are best utilized when they can be controlled as to their direction and depth of coagulation or vaporization, which preferably requires that they be used under direct vision. Unfortunately, at the present time, there is no way of visually observing intra-arterial use of lasers except with a procedure where the blood is replaced with a clear fluid such as a normal saline solution. This procedure involves injecting a bolus of the clear fluid at the tip of the laser fiber immediately prior to irradiating the obstruction with laser energy. The bolus provides a clear field of view for short period of time which enables a physician to view the obstruction prior to irradiating it with the laser. Unfortunately, the clear field is quickly obscured by the flow of blood through the vessel, and there is rarely enough time to re-position the laser fiber if such is necessary.
Attempts to create and maintain a blood-free segment in a blood vessel have been made with a balloon which is inserted into a blood vessel and then inflated to create an obstruction to blood flow. It was thought that a blood-free segment on the downstream of the balloon obstruction would materialize when the balloon was inflated to obstruct blood flow. However, blood from small downstream tributary arteries (i.e., on the downstream side of the balloon obstruction) quickly back-filled into the area adjacent the balloon, thereby preventing the formation of the blood-free segment.